The self-proclaimed Islamic State took control of the Syrian city of Raqqa from opposition rebel groups in 2014, treating it as the capital of a caliphate spanning large parts of both Syria and neighbouring Iraq.
But last November, Kurdish YPG and Arab forces, collectively known as the Syrian Democratic Forces, began encircling the city, with air support from the United States.
Now, several days into operation Wrath of Euphrates ground forces are reportedly making gains from the north, south and east.
And a new online video purports to show fighters from the forces at the ruins of the thousand-year-old Harqalah fortress outside Raqqa.
It apparently has been captured from IS, known also as Daesh.
"We are in the city of Raqqa, the province of Raqqa. This the first province and the first centre of Daesh in Syria, because they have two centres, one in Iraq in Mosul and the city of Raqqa. This area has been under the control of Daesh for more than five to six years, and they were fortified here. People faced a lot of unfairness. We, in response to the calls made by people, have come to liberate Raqqa, and we liberated two villages, the villages of Rabee and al-Jazra."
The US-led military coalition estimates thousands of IS fighters could still be inside Raqqa, signalling a potentially difficult fight for incoming forces.
Brett McGurk, the US special envoy to the coalition, says the attack against IS is set to accelerate.
He says IS has already suffered massive losses in Iraq, where a campaign to retake the stronghold of Mosul is in its ninth month.
"In this campaign against Daesh, in operations that we as a coalition have supported in Iraq and Syria, Daesh has now lost almost 55,000 square kilometres of territory that it used to control. Over 4 million people that used to be living under Daesh are now free."
The US move to arm Kurdish fighters in Syria has angered Turkey, which sees the YPG as linked to the Kurdistan Workers Party, or PKK.
Turkey has banned the group for its decades-long fight for independence on Turkish territory.
And Turkey says it is prepared to act immediately if any perceived threats arise from operations to take control of Raqqa.
It fears Kurdish participation could embolden the PKK across the border.
A political analyst in Syria, Sarikis Kassargian, says the Raqqa front is a source of US tension with Turkey and Russia, which backs Syrian government forces reportedly also advancing on the city.
"I don't think that there is an agreement about Raqqa with the US and Russia. More than that, I think that Raqqa is a problem in the relations, between the US and Russia on one side and between the US and Turkey on another side. But it seems that America's new administration and Trump insist to make a new change, or to make border changes, in this area. So this is why he has pushed the SDF to begin the Raqqa liberation."
Russia is hosting the United Nations' special envoy for Syria, Staffan de Mistura, ahead of a new round of scheduled peace talks in Astana, Kazakhstan.
Co-sponsored by Iran and Turkey, the negotiations were expected to focus on so-called "de-escalation zones."
Mr De Mistura, visiting Moscow for the third time this year, has urged Russia to coordinate efforts at the talks with those happening in Geneva under UN auspices.
"We want to share together our own thoughts about the next round of Geneva talks and how the Astana discussions will be, in a way, connected and connectable both, since, without a good de-escalation process, the Geneva talks will be difficult but, without the Geneva progress, there will be no horizon. So they are very closely interconnected."
